The International Astronomical Union (IAU; French: Union astronomique internationale, UAI) is a collection of professional astronomers, at the PhD level and beyond, active in professional research and education in astronomy.[1] It acts as the internationally recognized authority for assigning designations to celestial bodies (stars, planets, asteroids, etc.) and any surface features on them.[2]

The IAU is a member of the International Council for Science (ICSU). Its main objective is to promote and safeguard the science of astronomy in all its aspects through international cooperation. The IAU maintains friendly relations with organizations that include amateur astronomers in their membership. The IAU has its head office on the second floor of the Institut d'Astrophysique de Paris in the 14th arrondissement of Paris.[3] Working groups include the Working Group for Planetary System Nomenclature (WGPSN), which maintains the astronomical naming conventions and planetary nomenclature for planetary bodies. The IAU is also responsible for the system of astronomical telegrams which are produced and distributed on its behalf by the Central Bureau for Astronomical Telegrams. The Minor Planet Center also operates under the IAU, and is a clearinghouse for all non-planetary or non-moon bodies in the solar system. The Working Group for Meteor Shower Nomenclature and the Meteor Data Center coordinate the nomenclature of meteor showers.

The IAU was founded in 1919, as a merger of various international projects including the Carte du Ciel, the Solar Union and the International Time Bureau (Bureau International de l'Heure). The first appointed President was Benjamin Baillaud. Pieter Johannes van Rhijn served as president from 1932 to 1958. In the IAU Information Bulletin No. 100,[4] twelve of the fourteen past General Secretaries since 1964, each one in office for the three years between General Assemblies, recall the IAU history with its difficulties, e.g. with Soviet bloc officials, with the Greek military junta, and the reasons behind the unpopular decision to hold an additional Extraordinary General Assembly in Poland on the occasion of Nicolaus Copernicus' 500th birthday in February 1973, shortly after the regular GA in Australia.[a]

The IAU counts a total of 11,438 members, most of them being active individual members, professional astronomers from 96 countries worldwide.[5] 86% of all individual members are male, while 14% are female, among them the union's former president, astronomer Catherine J. Cesarsky.

The sovereign body of the IAU is its General Assembly, which comprises all members. The Assembly determines IAU policy, approves the Statutes and By-Laws of the Union (and amendments proposed thereto) and elects various committees.

The right to vote on matters brought before the Assembly varies according to the type of business under discussion. The Statutes consider such business to be divided into two categories:

issues of a "primarily scientific nature" (as determined by the Executive Committee), upon which voting is restricted to individual members, and

all other matters (such as Statute revision and procedural questions), upon which voting is restricted to the representatives of national members.

On budget matters (which fall into the second category), votes are weighted according to the relative subscription levels of the national members. A second category vote requires a turnout of at least two-thirds of national members in order to be valid. An absolute majority is sufficient for approval in any vote, except for Statute revision which requires a two-thirds majority. An equality of votes is resolved by the vote of the President of the Union.

The IAU includes member organizations from 73 countries (so-called national members).[6]

Since 1922, the IAU General Assembly meets every three years, with the exception of the period between 1938 to 1948, due to World War II. After a Polish request in 1967, and by a controversial decision of the then President of the IAU, an Extraordinary IAU General Assembly was held in February 1973 in Warsaw, Poland, to commemorate the 500th anniversary of the birth of Nicolaus Copernicus, soon after the regular 1973 GA had been held in Australia.

The XXVIth General Assembly of the International Astronomical Union was held from 14 to 25 August 2006 in Prague, Czech Republic. On 15 August the Assembly decided to restore to individual members the right to vote on scientific matters, which had been removed from them at the XXVth Assembly in 2003. Among the business before the Assembly was a proposal to adopt a formal definition of planet. During the General Assembly the text of the definition evolved from the initial proposal that would have created 12 known planets in the Solar System (retaining Pluto and adding Ceres, Pluto's largest moon Charon, and Eris) to the final definition of a planet resolution that was passed on 24 August by the Assembly, which classified Ceres, Eris and Pluto as dwarf planets, and reduced the number of planets in the Solar System to 8. The voting procedure followed IAU's Statutes[7] and Working Rules.[8] The General Assembly lasted 12 days and had 2412 participants,[9] most of them for only part of the duration of the Assembly. 424 of the 9785 individual IAU members attended the Closing Ceremony on 24 August 2006. Following the Closing Ceremony, parts of the scientific community did not agree with this ruling, especially the specific wording of the resolution, and criticized IAU's authority to name celestial bodies. In the ensuing public debate, a number of laypersons expressed (at times strong) disagreement with the vote. Another, less vocal, fraction of the scientific community backs the resolution, including the discoverer of the dwarf planet Eris, Mike Brown.

A final decision was made, announced 11 June 2008, for acceptance of the term plutoid and its official IAU definition:

Plutoids are celestial bodies in orbit around the Sun at a semimajor axis greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighbourhood around their orbit. Satellites of plutoids are not plutoids themselves.[10]

Commission 46 is a Committee of the Executive Committee of the IAU. As a prestigious international scientific union, the IAU plays a special role in the discussion of astronomy development with governments and scientific academies and in interceding about such matters at the highest levels. The IAU is affiliated with the International Council of Scientific Unions (ICSU), a non-governmental organization representing a global membership that includes both national scientific bodies and international scientific unions. When appropriate, the President and officers of the IAU are proactive in persuading the authorities of the importance of astronomy for development and education and in encouraging countries to become members of the IAU. A strategic plan for the period 2010-2020 has been published.[11]

The Commission seeks to further the development and improvement of astronomical education at all levels throughout the world, through various projects initiated, maintained, and to be developed by the Commission and by disseminating information concerning astronomy education at all levels. Part of Commission 46, the Teaching Astronomy for Development (TAD) program is intended to help enhance astronomy education significantly in countries where there is currently very little on offer. TAD operates on the basis of a proposal from a professional astronomy organization or a contract between the IAU and an academic institution, usually a university.

The IAU has launched in 2009 the Galileo Teacher Training Program (GTTP), a Cornerstone project of the International Year of Astronomy 2009, among which Hands-On Universe is a major partner. Hands-On Universe is now officially included in the Astronomy for the Developing World Strategic Plan 2010-20 of IAU, under Section 3.4.2 Astronomy for Children and Schools. During the next decade the IAU will concentrate more resources on education activities for children and schools designed to advance sustainable global development.

The GTTP is concerned with the effective use and transfer of astronomy education tools and resources into classroom science curricula. By training a worldwide network of "Galileo Ambassadors" who will train new "Galileo Teachers" the effect of the program will be multiplied. The GTTP is closely affiliated with the Global Hands-on Universe Program.

Outreach to teachers will involve the provision of training courses, development and translation of materials and harnessing global technological resources in the service of primary and secondary education. A specific goal will be to provide expertise for at least one teacher training course in each region every year, to be organized together with the regional coordinators.

^Cornelis de Jager, 16th GS, 1970-1973: I had to organise in one year two General Assemblies, one in Sydney, Australia, and another one, a so-called Extraordinary General Assembly, a month or so later in Poland. I was strongly against the decision to have that latter meeting ... When, in 1967, I attended my first meeting of the Executive Board, with Otto Heckmann as President ... I learned that the 1973 GA would be held in Sydney ... A severe complication then arose. During the time of Heckmann’s presidency it so happened that we got a request from and a visit by the grand old lady of Polish astronomy, Ms. Wilhelmina Iwanowska. She brought to our memory that 1973 would be the year of the 500th birthday anniversary of Copernicus. She proposed that the IAU would in that year have a General Assembly in Poland ... At that time Ms. Iwanowska, who certainly was a clever politician, made a slip. She replied that in any case very few astronomers from eastern Europe – we used to call it the Soviet bloc – were planning to make that long and costly trip. It left us with an unanswered question: was that perhaps the main reason? I recall how difficult the situation was for Heckmann, our German President. He was a truly honest and sensitive man who – slightly more than twenty years after the war – very well realized what Germany had done to Poland. He found it difficult to refuse a request from Poland and that was the main reason for him to consent. I was strongly against, but the voice of an Assistant General Secretary is not as important as the President’s. So the decision was taken. Many astronomers disagreed. I learned during my term (1970-1973) how much opposition arose when the news spread around. Several astronomers, mainly from the US, angrily wrote to me that they would never, repeat: never again join a General Assembly, and that was what they actually did. - IAU Information Bulletin No. 100, July 2007, p. 9